Many implantable medical devices require percutaneous communication. That is, in particular regard to implantable drug infusion devices, such devices often require the drug supply to be replenished. Typically, such replenishment is accomplished by inserting a needle through the skin and into the septum of a drug reservoir in such a device.
Because such a device is implanted and thus not able to be directly seen, care must be taken to ensure that the needle is properly placed into the device before injection. If the needle misses the device and, in particular, misses the drug reservoir in the device, the drugs will be immediately dispensed in the body, having potentially dire consequences for the patient. Moreover, if the needle is not fully placed through the septum and into the drug reservoir, the drug reservoir will not be adequately filled, also having potentially dire consequences for the patient.
Previous attempts have been made to accurately locate and identify implanted devices and, in particular, septum loading to the drug reservoir of implantable drug infusion devices. For example, Celcontrol, Inc. advertised an implantable vascular access device which required the attachment of an electrode to the skin and the attachment of a wire to the hypodermic needle to create a circuit for locating the implantable device. Such a system, besides having more complexity than desired, did not provide an accurate location of the needle in relation to the device without first inserting the needle through the skin. U.S. Pat. No. 5,171,228 disclosed a further system which required an RF transmitter and a transmitting antenna. Such a system, to date, has not proven practical or provided an acceptable precision for locating the implantable device. Thus, there exists a need for a simple device and technique for sensing the position of an implanted device and, in particular, of a drug reservoir septum, without first requiring the skin to be punctured or additional electrode attachments to be made to the patient.